will have or would have

 

We use the perfective will have when we are looking back from a point in time when something will have happened.

By the end of the decade scientists will have discovered a cure for influenza.
I will phone at six o’clock. He will have got home by then.

or looking "back" from the present:

Look at the time. The match will have started.
It’s half past five. Dad will have finished work.

We use would have as the past tense form of will have:

I phoned at six o’clock. I knew he would have got home by then.
It was half past five. Dad would have finished work.

We use would have in past conditionals to talk about something that did not happen:

If it had been a little warmer we would have gone for a swim.
He would have been very angry if he had seen you.
 

Exercise

Comments

Hi LE Team,

Is it true that we can use the future perfect continuous to express an assumption about what might have been happening/what we think was happening at a point in the past?

That boy is crying. He'll have been quarreling with his brother, as usual.

And what's the difference with "He must have been quarreling"...if any?

Thanks a lot in advance for clarifying this.

Hi Knightrider,

You are correct that we can use will have in that way.  Remember, English does not have a future tense as such, but rather has a range of different ways of expressing future time.  One way is by using modal verbs such as 'will', 'must', 'should' and so on, and these modal verbs can be used with other time references including, as perfect modals, past time.

The difference between the two is quite subtle and they are largely interchangeable. Both are used deductions based on (present or past) evidence, but a speaker will tend to use 'will have' when they wish to convey a sense of typical or habitual behaviour.

I hope that helps to clarify it for you.

Best wishes,

 

Peter

The LearnEnglish Team

happy new year to all!
i have question for the following sentence.
'you will all have heard the news last night'.
should i use 'would' instead of 'will' since refers to last night?

Hi nathanic,

Whether this sentence is correct with will or would depends on what you mean to say and/or on the context.

If I said "you will all have heard the news last night" without any particular context, it would mean something like "I assume that you all hard the news last night". This usage of will to express certainty or probability is the same as the meaning of must have on our certain, probable or possible page (under the Probability section).

If I said "you would all have heard the news last night" without any particular context, it would probably be part of a conditional structure to talk about something that did not happen, e.g. "you would all have heard the news last night if you had been watching television". This is explained above on this page.

Best wishes and Happy New Year!

Kirk
The LearnEnglish Team

Thanks Kirk,
another question if you don't mind.
if the sentence is past tense as the following,
It was all over the news yesterday, you would have heard it already.
i must use "would" instead of "will" right? Since the whole sentence is in past tense.
regards,
nathan

Hello Nathan,

Both 'will have' and 'would have' are possible here, but the meaning is different.

'It was all over the news yesterday, you would have heard it already [if you had watched the news]' - you didn't hear, because you don't or couldn't watch the news

'It was all over the news yesterday, you will have heard it already.' - I'm sure you heard it because I know you watch the news

One is an unreal past - a past which we know to be not true.  The second is a guess about the past which we believe or expect to be true.

As Kirk said in his reply, the context is key here, not just the time reference in the first part of the sentence.  It's quite possible to have a mix of time references, as you can see above.

I hope that helps to clarify it for you.

Best wishes,

 

Peter

The LearnEnglish Team

thanks peter, I get the meaning of using will have, but a bit unclear about the use of would have. Using the example above, It's half past five, dad will have finished work. If i said it, I am certain dad have finished his work.
As for this sentence,It was half past five, dad would have finished work. Does it carry two possibilities? one is that i am certain dad have finished work. i used would have because the whole sentence is in past tense form, or  the other  is that  dad actually didn't finish his work. (he would have finished if he hadn't taken a long break) 
or  perhaps if i want to go for the second meaning, the sentence should be like this? It was half past five, dad would had finished work.
pardon my grammar, thanks again.
regards,
nathan

Hello nathan,

With regard to 'will have', you are correct - the sentence means that we know, believe or expect that it is true.

With regard to 'would have' you are also correct that two meanings are possible:

It was half past five, dad would have finished work.

1) A past version of the 'will have' example above - imagine Sherlock Holmes making a deduction about what he believes happened in the past.

2) A hypothetical/untrue past result as a part of a conditional sentence, where the condition (the 'if' clause) is unspoken, probably because the context has made it clear.  The example of the 'if' clause you provide is a good one, and the sentence then has the form sometimes called the 'third conditional'.  You can find more information on conditional forms here.

The correct form is 'would have', not *'would had'*.

I hope that clarifies it for you.

Best wishes,

 

Peter

The LearnEnglish Team

Hi Peter, 
thanks for your help, I feel silly that I have written would "had". Ha.
regards,
Nathan

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